WateringTimesWatering plan, $19
Eucalyptus globulus, WUCOLS IV

How often to water blue gum in California

In July in the Central Valley, established blue gum in loam needs a deep watering about every 20 days: about 55 gallons each time under a 10 foot canopy, about 19 gallons a week. Blue gum is a fast growing eucalyptus from southeastern Australia that can reach 50 to 150 feet. Its bark sheds in long strips, and its aromatic adult leaves are long and lance-shaped, while young growth carries rounded, bluish leaves. It has escaped to become invasive along the California coast and affects fire danger where it spreads.

TreeRated for 5 of 6 zones

How often to water blue gum, month by month

Your city
Canopy width
10 ft
Your soil

Type your city above and the days between waterings and the gallons appear here, worked out from your city's climate table. Or read the figures by climate zone further down.

Every month, on your water days. The personal plan prints this for blue gum and the rest of your yard, on the days your water supplier allows.Get the plan for $19

How this is worked out: established roots fill the top 1.5 feet of soil, and you water again when that soil has dried halfway. Loam soil holds about 1.5 inches of water per foot. Water the whole area under the branches, and skip a watering after a good soaking rain.

Which soil do you have?

Dig down a few inches, take a handful of moist soil and squeeze it.

  • Sandy: gritty, falls apart when you open your hand, will not form a ball.
  • Loam: forms a soft ball that crumbles when you poke it.
  • Clay: forms a firm, sticky ball and squeezes out into a ribbon between thumb and finger.

Still not sure? Pick loam. Most garden beds sit between sand and clay.

How to measure canopy width

A tree with its canopy width marked across the widest branches and the circle under it shaded blue

Measure across the branches, from the tips of the outer leaves on one side to the tips on the other. A tape works, or pace it out.

Water the whole circle under the branches, shown in blue. The gallons here cover that circle.

A wider canopy means more gallons each watering, not more waterings. While the tree is young, measure again each spring.

How to tell it needs water

  • Soil dry a foot down beneath the canopy during a long summer drought signals that a deep, slow soak is due
  • Holes in the bark with stains or oozing liquid point to longhorned borers, which favor water stressed trees
  • A thinning, yellowing crown in late summer can follow seasonal water stress, so check deep soil moisture
  • Mushrooms or decay at the root crown after prolonged wet soil point to root rot from waterlogging
  • Bark peeling away in long strips is normal for this tree and not a sign of stress

How to water it

  • Water slowly with drip emitters spread across the root zone so moisture sinks a foot or more
  • Irrigate infrequently and only in long dry spells, letting the soil dry between deep soaks
  • Keep water from pooling at the root crown, since prolonged waterlogging invites root rot
  • Spread wood chip mulch over the root zone, keeping it clear of the trunk base
  • Move emitters outward as the canopy widens

Through the seasons

A young blue gum needs deep watering through its first summers while roots spread. Established trees need only occasional deep soaks in long dry spells, but water stress in hot summers invites longhorned borers. WUCOLS rates blue gum low water on the north-central coast, in the Central Valley and on the south coast. It rates moderate water in South Inland and the low desert. WUCOLS marks it as not suited to the high desert. This evergreen flowers in winter or early spring, and winter rain usually covers it on the coast and in the Central Valley.

In pots

Blue gum is a giant tree, so a container suits only a seedling for a short time. Its invasive habit is also a reason to keep it away from open land. Use a deep pot with drainage holes and a well-drained mix. Check the mix 2 inches down every few days in summer and water when it is dry there. Let water drain, then empty the saucer. In winter, water only when the mix begins to dry.

1 Your climate zone six WUCOLS zones, each from its own reference city
1.07gal per sq ft in JulyLow water use in the Central Valley zone
A year
6.84 gal per sq ft
Reference
Sacramento climate table
Counts
Plant need, before sprinkler losses
0.711.42.12.90.16JAN0.26FEB0.43MAR0.61APR0.83MAY0.99JUN1.07JUL0.95AUG0.72SEP0.47OCT0.22NOV0.14DEC0.711.42.12.90.16JFM0.61AMJ1.07JAS0.47OND
Gallons per square foot per month, Central Valley. Peak 1.07 in Jul, 6.84 a year.

Monthly water need by climate zone

Blue Gum: gallons per square foot per month, by WUCOLS climate zone

MonthN. CoastC. ValleyS. CoastS. InlandHi DesertLo Desert
Jan0.150.160.310.78–0.78
Feb0.210.260.320.87–0.93
Mar0.350.430.461.3–1.52
Apr0.470.610.561.61–1.95
May0.580.830.641.95–2.45
Jun0.640.990.692.29–2.79
Jul0.641.070.792.51–2.85
Aug0.60.950.742.33–2.6
Sep0.50.720.61.86–2.08
Oct0.350.470.461.33–1.49
Nov0.190.220.330.9–0.96
Dec0.120.140.260.68–0.68
Year4.86.846.218.41–21.08

How this is worked out: the WUCOLS water rating for each zone times that zone’s climate for the month. A dash means WUCOLS does not rate the plant there. The figures are what the plant uses, before sprinkler losses.

Plants with the same water needs 16

Rated low water in the Central Valley, like blue gum. Plants that drink alike can share one valve and one schedule.

Olive TreesOlea europaea ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyFig TreesFicus carica ssp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyCrape MyrtleLagerstroemia spp., hybrids & cvs.low water, Central Valley1.07 gal/sq ft in JulyAloeAloe spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyPomegranate TreesPunica granatumlow water, Central Valley1.07 gal/sq ft in JulyEucalyptusEucalyptus polyanthemoslow water, Central Valley1.07 gal/sq ft in JulyPine TreesPinus canariensislow water, Central Valley1.07 gal/sq ft in JulyJunipersJuniperus spp. & cvs.low water, Central Valley1.07 gal/sq ft in JulyTexas Red OakQuercus buckleyilow water, Central Valley1.07 gal/sq ft in JulyPortuguese OakQuercus faginealow water, Central Valley1.07 gal/sq ft in JulySoapbark TreeQuillaja saponarialow water, Central Valley1.07 gal/sq ft in JulyNecklace TreeSophora affinislow water, Central Valley1.07 gal/sq ft in JulyBailey AcaciaAcacia baileyanalow water, Central Valley1.07 gal/sq ft in JulySilver WattleAcacia dealbatalow water, Central Valley1.07 gal/sq ft in JulyGreen WattleAcacia decurrenslow water, Central Valley1.07 gal/sq ft in JulySydney Golden WattleAcacia longifolialow water, Central Valley1.07 gal/sq ft in July
Minutes for your sprinklers

Turn this into minutes on your water days

Every city page has a calculator that takes blue gum, your sprinkler type and the month, and gives the minutes per water day for that supplier's schedule. Or put it in a zone of the personal watering plan and get all twelve months printed.

Questions people ask

How often should I water blue gum in summer?

In July, established blue gum in loam needs a deep watering about every 20 days in the Central Valley, about every 27 days on the south coast and about every 9 days in the South Inland zone. Sandy soil holds less water, so waterings come closer together. Clay stretches them. Check the soil before each watering and skip one after a soaking rain.

How much water does blue gum need per day?

In July in the Central Valley, established blue gum needs about 2.7 gallons a day under a 10 foot canopy and about 11 gallons a day under a 20 foot canopy. Give it in deep waterings spread days apart rather than a little every day, so the whole root zone gets wet.

Does watering for blue gum change across California?

Yes. WUCOLS rates blue gum separately for each of the six California climate zones: low water in the North-Central Coastal zone, low water in the Central Valley zone, low water in the South Coastal zone, moderate water in the South Inland zone, not suited to this region in the High and Intermediate Desert zone, moderate water in the Low Desert zone. The monthly table above shows how the same rating translates into different gallon amounts as reference evapotranspiration changes.

Is blue gum invasive in California?

Yes. It has escaped cultivation and become invasive along the coast. Where it spreads, it affects fire danger, groundwater, native plants and wildlife. Avoid planting it near open land.

What are the holes and sap stains on my eucalyptus?

Holes in the bark with stains or oozing liquid are common signs of longhorned borers. These beetles mostly attack stressed trees, and blue gum is among the more susceptible species. Deep, infrequent watering in drought helps the tree resist them.

When should I prune blue gum?

Do routine pruning in December and January, when the borer beetles are not active. Remove infested branches right away at any time. Spread heavy limb removal over several years.

Can you overwater blue gum?

Yes. Prolonged waterlogging, especially around the root crown, invites Armillaria and Phytophthora root rots. Apply water slowly and let the soil dry between soakings.

Why does blue gum have two kinds of leaves?

Young growth carries oval, bluish gray-green leaves, while mature branches bear long, lance-shaped, dark green leaves that hang down. Both forms are normal on the same tree.

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Sources